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Lecture

ANT100Y1 Lecture Notes - Radionuclide, Poaceae, Rock Art


Department
Anthropology
Course Code
ANT100Y1
Professor
Christopher Watts

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Concerned with everyday practices and everyday life
The matrices in which artifacts, ecofacts, sites and other human -manufactured features or results
of past human action are found
Archaeological Record
Observed material culture
Unobserved human/non-human activity
Interpretation/explanation of human activity
Three Typical Elements of Archaeological Research
Spatial (positions of artifacts): activity areas, sites, regions
Material Evidence
Any portable object whose form has been shaped (i.e., manufactured or modified) by way of
human activity
Things that have been modelled and shaped
Example: Acheulian Hand Axe from Gilan, Iraq; Funerary mask of Tutankhamun
Artifact
Nonportable material evidence of human activity (e.g., hearths, storage pits, postholes)
Example: Kelly Site Excavation Plan; Rock art; Pyramids, Giza
Feature
Non-artifactual material evidence of human activity
Can be further subdivided into Macrofossils and Microfossils
Visible to the naked eye, e.g., kernel of corn
Can be retrieved through flotation or normal excavation procedures
Water separation of soil matrices
Used primarily to recover macrofossils
Lighter materials float to the surface, caught in sieves
Flotation Device
Macrofossils
e.g., pollen, phytoliths found in soils or residues adhering to artifacts
Retrieved through mechanical and chemical disaggregation
Visible only under high-power magnification, 200x or greater
Example: Poaceae (grass) pollen grains
Microfossils
Ecofacts
Can be defined in a number of ways
Artifacts
Ecofacts
Features
Example: a typical Iroquoian village, ca. AD 1500; Iroquoian longhouse in plan view
Usually consists of a collection of activity areas containing any of the following:
Archaeological Site
Physical location in three dimensional space
Site level: grid system
Regional level: map co-ordinates, settlement features (e.g., roads, towns)
Provides us with recording that spatial dimension
But without knowing one thing came from, there is not much to say about that object
Provenience (Provenance)
e.g., curating/discard of objects
Materials were brought to a central area (in this case a
midden) for deposition
Human agencies
e.g., soil composition, environment, temperature, disturbance
by animals (taphonomic processes)
Examples: Floods, predation
Things that took place in the past
Natural agencies
Affected by:
Site Formation Processes
Normally begins with a surface collection (if site is ploughed or
disturbed)
Datum and grid
The spatial distribution of artifacts on the surface of a site
is recorded with reference to a fixed point (datum)
This produces accurate maps which can then be used to
guide the excavation
Surface collection
When excavating, we record subsurface features and the
location of artifacts in a similar fashion...
With reference to a grid system (based on Cartesian
coordinates: x and y axes
Uncover and remove layers (stratas) from youngest
to oldest, simultaneously, across a wide area
Open-area, areal o horizontal excavations
Focused on a single, small portion of the site
Units separated by baulks
You can employ this if you don't have a lot of
people, money or time
Grid-and baulk or vertical excavations
Types of Excavations
Considerations: aperture size of mesh
Examples: Screen
Stratigraphy: the analytical process by which we order layers
and features chronologically; how sites are formed in the
record
Sediments are deposited on top of pre-existing sediments
Based on the Law of Superposition
Excavation: recovering archaeological data
Subsurface Techniques
Stratigraphy is a relative dating method
Levels (and, by extension, the artifacts, ecofacts, and features contained in them) can be ordered through
time based on their stratigraphic position
Tree-ring dating of preserved wood
Chronologies based on overlapping ring sequences
Cannot be used in tropical regions
Confined to certain tree species
Limitations:
Dendrochronology
Radioactive isotope or 'variety' of carbon which forms in the atmosphere
Absorbed by plants during photosynthesis
Absorbed by animals when they eat plants
After death, 14C decays at a known rate--its "half-life"
5730 +/- 40 years
Libby's calculations were based on a 'curve of knowns'
Cheapest of the two, but...
Is not as sensitive as AMS
Requires larger samples (~10 to 500 grams of material)
More expensive, but more accurate
Can get away with smaller samples (~100 mg or less)
Fewer labs
AMS: direct counting of 14C atoms, not based on decay per unit of time
Conventional: measures rate of decay per unit of time
Necessary because of atmospheric fluctuation in carbon levels through time
Curves based on comparison of sample 14C dates with dates obtained through other
means (e.g., dendrochronology)
Calibration Curves
Must be calibrated
Radiocarbon Dating
In this case 40K to 40Ar
Same principle as 14C: radioactive decay
Half-life is around 1.3 billion years
Gives an estimate of volcanic rock formation
Geological dates on rock samples
Indirect form of dating
Potassium-Argon Dating
Works on pottery and HT cherts/flints
Electrons released during firing
After firing, surrounding electrons of uranium, thorium and potassium become re-absorbed
(trapped)
Re-heating object releases electrons, which emit light (TL) as they escape
Advantages: can be used on pottery and heat-treated flint/chert older than 50000 years
Disadvantages: less precise than 14C; requires sample of surrounding matrix (sediment)
Thermoluminescence (TL) Dating
There are other methods known as absolute dating methods
Dating Techniques
Finding Archaeological Sites
Field walking: used to survey ploughed areas; very efficient
Testpitting: used to survey areas that cannot be examined by other methods
Aerial photography: great tool for finding sites, or identifying areas of high potential;
works well when there are large-scale landscape features
satellite imaging
Resistivity: measures the resistance of the ground to an electrical current;
current passes more quickly through wet ground than dry ground
Magnetometry: measures magnetic fields below the earth`s surface; some
archaeological features (e.g., building materials with iron, hearth events) have
their own magnetic fields
Ground Penetrating Radar (GPR): uses radio waves to detect subsurface
features; the stronger the bounce, the bigger the object or feature; the longer it
takes for the bounce to return, the deeper the object or feature
Only method to provide data along vertical axis of soil matrix
Cost-effective, efficient and accurate
Non-destructive and non-invasive
Devices are relatively portable
On-site real time data display
Benefits:
Remote sensing
Surface techniques
Field Methods
Note: A number of sites are found by accident!
Archaeological Data and Dating
October-28-10
6:00 PM
ANTHROPOLOGY Page 1
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